What is the difference between atmospheric science and artificial influence on the atmosphere?

Measures to artificially promote precipitation in clouds. Also known as artificial precipitation enhancement. According to the physical characteristics of different clouds, catalysts such as water droplets, salt powder or solution droplets, silver iodide or solid carbon dioxide (dry ice) are mainly scattered into the clouds (see cloud seeding catalyst), so that cloud droplets or ice crystals increase to a certain extent and fall to the ground to form precipitation. This is the most common experiment in weather modification. In a thunderstorm cloud, the amount of liquid and solid water reaches the order of millions of tons. Because the water in the cloud is constantly replenished and updated, the total condensed water is even greater. Clouds and precipitation are important water resources. Natural clouds are composed of cloud droplets, the size of which is only 0.0 1 mm, which are suspended in the air and cannot fall. Only when it is transformed into precipitation particles with the scale of 1 mm such as rain, snow or graupel can it fall to the ground. Many natural clouds don't precipitation, even if precipitation clouds generally only 20 ~ 80% of water can be converted into precipitation, so a lot of water resources can't be fully utilized. The precipitation efficiency of a cloud depends not only on the macroscopic conditions of the cloud (see cloud dynamics), but also on the microphysical process of cloud droplets transforming into precipitation particles (see cloud and precipitation microphysics). Under certain conditions, the microphysical process of artificially influencing clouds can stimulate clouds that can't naturally precipitation, and can also make those clouds that have more water supply and can often naturally precipitation, improve precipitation efficiency and increase precipitation. However, cloud energy that can't naturally precipitation can supply less water, so the economic value of artificial catalysis is limited. Principles and Methods Leng Yun Catalysis The concentration of ice crystals plays an important role in the process of cold cloud precipitation with the temperature below 0℃. According to the measured data and theoretical estimation of precipitation particle concentration, precipitation efficiency will be higher only when the ice crystal concentration reaches 1/L or higher. For natural clouds with low precipitation efficiency due to insufficient ice crystal concentration, if ice catalyst is sown in the supercooled part, the ice crystal concentration can be increased. Each gram of dry ice or silver iodide can produce more than 10 12 ice crystals. If you use a few hundred grams, the concentration of ice crystals in the clouds of dozens of cubic kilometers can reach 10/ liter. These artificial ice crystals grow rapidly through the Bergeron process, which promotes the cold cloud precipitation process and increases precipitation. Statistical analysis of some rigorous experiments shows that Leng Yun catalysis can increase precipitation 10 ~ 20%. If the concentration of artificial ice crystals is large, the average scale of snow crystals will be small, and it will take a long time to fall from the clouds to the ground. Under the action of airflow, they will fall further downwind, changing the distribution of precipitation. Warm Cloud Catalysis In a warm cloud with a temperature higher than 0℃, precipitation is mainly generated during the collision of cloud droplets. The bigger the cloud droplets are, the faster they collide and grow. The calculation shows that when the radius of cloud droplets exceeds 0.04 mm, they can quickly collide and grow into raindrops. In the natural cloud with insufficient concentration of large cloud droplets, sowing a large number of water droplets with radius greater than 0.04 mm can promote the precipitation process. The calculation shows that millions of large cloud droplets can be formed per gram of water, and several tons of water are needed to catalyze 10 cubic kilometers of clouds. If particles or solution drops of hygroscopic substances with a certain size are sown in the cloud, they can absorb the water in the cloud and quickly grow into large cloud drops, so the amount of catalyst needed is less than one tenth of that of water. In addition to sowing clouds, some people in France and the Soviet Union also tried to heat the ground to cause artificial updraft, trying to stimulate or increase precipitation under certain meteorological conditions. Some people in the United States imagine using asphalt or carbon black to absorb solar radiation, raise the local air temperature and promote the development of clouds to increase precipitation. Some people in China have studied the influence of explosion on precipitation. The research of these artificial precipitation enhancement methods is still in the exploratory stage. Dynamic catalysis produces a large number of ice crystals in clouds through Leng Yun catalysis, and the released latent heat will change the macro-dynamic process of cumulus clouds and increase precipitation. This is a progress of artificial precipitation enhancement experiment in 1960s. The velocity of updraft in cumulus clouds is mainly determined by the buoyancy generated by the temperature difference between inside and outside the clouds. There are a lot of supercooled water droplets in the exuberant cumulus. When a large number of ice-forming catalysts are sown in this cloud, supercooled water droplets can freeze and release latent heat, and water vapor also releases latent heat when it condenses on the surface of ice particles. It is estimated that these two kinds of latent heat are enough to raise the local temperature in the cloud by about 0.5℃, thus increasing buoyancy, promoting the rising speed of some cumulus clouds, expanding the clouds and prolonging their life. In this way, the total amount of water entering the cloud will increase, and the precipitation will also increase. Although the catalyst used in kinetic catalysis is the same as that used in general Leng Yun catalysis, the emphasis is different, and the amount of catalyst used in kinetic catalysis must be greatly increased to be effective. Cumulus kinetic catalysis was tried as early as 1950s, but the well-designed cumulus kinetic catalysis experiment didn't begin until 1963. J Simpson's random experiment in Florida, USA, showed that the cumulus cloud top increased by 65438 0.6 km on average, and the average rainfall increased by 65438 0.7 times. He pointed out that the increase of cloud top after catalysis is closely related to atmospheric stratification (see atmospheric static stability). Other countries and regions have done similar experiments, but the results are different. A random experiment of dynamic catalytic cumulus population was conducted in the whole region, and the preliminary results showed that it had the effect of precipitation enhancement. The effect of catalytic artificial precipitation enhancement in Leng Yun is closely related to the natural conditions of clouds. As far as Leng Yun catalysis is concerned, the temperature condition in the cloud is very important. As far as the whole cloud is concerned, the cloud top temperature is generally the lowest, which is often used as a parameter to estimate the concentration of natural ice crystals in the cloud. When the cloud top temperature is low enough, a large number of ice crystals often form in the clouds. At this point, by manually adding ice crystals, the effect is not significant. On the other hand, if the cloud top temperature is too high, the ice-forming ability of silver iodide and other catalysts is too low, which is not conducive to artificial catalysis. Therefore, when Leng Yun catalytic method is used to increase precipitation, cloud top temperature should not be too high or too low. The statistical analysis of some experimental results of artificial precipitation enhancement in topographic clouds and cumulus clouds shows that the effect of artificial precipitation enhancement is obvious when the cloud top temperature is at-10 ~-25℃, and this optimal temperature range is called cloud seeding temperature window. In view of the complexity of precipitation process, it is necessary to study the most favorable temperature conditions or other conditions in various clouds when using different catalytic technologies. Numerical simulation describes and calculates the precipitation process and artificial catalysis process of clouds with mathematical and physical equations, and simulates the artificial influence process of various catalysis technologies under different conditions with numerical calculation methods to study the principle, technology and effect of catalysis. Because of the natural variability of clouds and precipitation, the research period of field experiments is very long and the cost is very high. A strictly designed experiment (some catalytic procedures, technologies, etc.) usually takes several years. ) to evaluate its effect. If we want to compare the effects of different catalytic technologies and choose the best experimental design, it will take longer. Therefore, it is very important to provide a basis for practical experiments and theoretical research through numerical simulation. Simpson used cumulus numerical simulation to calculate the development height of natural clouds in 1960s, and assumed that dynamic catalysis made water droplets in clouds freeze at a higher temperature than natural processes, releasing latent heat, thus calculating the development height of cumulus after catalysis. The measured results of the test are quite consistent with the model calculation. This provides a scientific basis for the principle of kinetic catalysis and the selection of experimental clouds. With the popularization of computer, many countries have carried out many numerical simulations on various artificial precipitation enhancement experiments. Although they greatly simplify the actual process and have limitations in different aspects, combining with field experiments can shorten the test period of evaluating the effect of artificial precipitation enhancement, thus becoming an important part of experimental research on artificial precipitation enhancement. Generally speaking, the method of artificial precipitation enhancement can only play a role when the natural cloud has fallen or is close to falling. Because of the natural variability of precipitation, it is difficult to evaluate the effect of artificial precipitation enhancement. The precipitation increased by artificial catalysis is the difference between the actual precipitation after catalysis and the natural precipitation without catalysis. The actual precipitation can be measured, but whether the natural precipitation can be correctly evaluated becomes the key to the effect test. In the case of insufficient understanding of the physical laws of precipitation, we mainly rely on statistical methods to evaluate the natural possible precipitation. In the initial statistical test methods, regression statistics are mostly used, and an area near the artificially catalyzed target area is selected as the control, and the regression equation of precipitation in the target area and the control area is established with historical data. Substituting the precipitation in the contrast area in the artificial precipitation enhancement experiment into the regression equation, the natural possible precipitation in the target area can be obtained, and then comparing it with the measured precipitation in the target area, the effect of artificial precipitation enhancement can be evaluated. Using this method to carry out the same experiment, selecting historical data from different comparison areas or different years for comparison, the results may be quite different, so the reliability of this method is not high. It is generally believed that random testing can avoid subjective bias and get a statistically credible evaluation. Random test is to divide the test opportunities (test units) suitable for artificial precipitation into two groups according to random rules (such as lottery): one group is catalytic observation, and the other group is only observation without catalysis for comparison. When there are enough test units, the natural conditions of the two groups of test units randomly determined should have only a very small systematic difference, and the systematic difference of the measured precipitation in the two groups of tests can be attributed to the result of artificial catalysis. Judging the catalytic effect, there is the possibility of success and failure. When judging that catalysis is effective but actually ineffective, this possibility is often expressed by the level of significance. The smaller the significance level, the higher the confidence of judging the catalytic effectiveness. In the experiment of artificial precipitation enhancement, the significance level is generally required to be less than 5%, that is, the reliability is greater than 95%. The effect of artificial precipitation enhancement is restricted by cloud and other conditions. It may have a significant positive effect under one condition and may be ineffective or even negative under another. Statistics generally do not consider conditions, and the analysis results are often not significant. When the test units are divided into several categories according to a certain index, sometimes more significant results can be obtained. For example, Leng Yun catalytic test, according to cloud top temperature classification, statistics show that it has a significant effect in a certain temperature range. From the research of artificial precipitation enhancement, it is not enough to evaluate the rainfall increase only, and it is necessary to have an exact understanding of each link of the whole physical process. For example, whether the catalyst has reached a certain concentration in a designated part of the cloud, and whether the concentration of ice crystals or large droplets has increased significantly. Observing and counting the changes of these macro and micro characteristics can analyze the effect of artificial catalysis from the physical process. This observation experiment is called the physical experiment of artificial precipitation enhancement effect. For example, in the Leng Yun experiment, it was observed that the concentration of ice crystals increased and the supercooled water droplets decreased after catalysis, indicating that artificial catalysis played a role in the microphysical process of clouds. It is generally believed that the scientific experiment of artificial precipitation enhancement must be carried out for a long time in strict accordance with the predetermined design according to the statistical requirements, and at the same time, the natural precipitation process and artificial catalysis process should be carefully detected and simulated on the spot, so that the experiment can have a solid physical foundation and statistical credibility. Because of the importance of water resources to the national economy, artificial precipitation enhancement experiment, as a potential means to develop water resources, has been widely valued. About 80 countries and regions in the world have carried out this experiment, among which the scale of experiments in the United States, Australia, China and the Soviet Union is relatively large. After 1958, ice-forming catalysts such as dry ice or silver iodide were spread into large-scale layered clouds by plane in northern provinces of China in an attempt to increase precipitation in winter and spring; China's southern provinces also use airplanes or anti-aircraft guns to scatter catalysts such as salt powder or silver iodide into cumulus clouds to increase precipitation during the summer drought. However, many basic problems in natural precipitation and artificial catalysis are still unclear, and there are still many difficulties in testing the effect of artificial precipitation.